The broad goal of this project is to understand the steps involved in the hormonal control of steroidogenesis. This includes the metabolic events that follow stimulation of specific receptors in steroidogenic cells by trophic hormones, including the coupling mechanisms between receptor occupancy and the sequence of events which leads to stimulation or inhibition of steroidogenic enzymes and androgen production. We have a) demonstrated that Leydig cell protein kinase behaves as a Type I enzyme on DEAE analysis, but has physical and functional characteristics that resemble the Type II enzyme of bovine myocardium; b) fractionated and analyzed Leydig cell populations, in which electron microscopic studies suggest that functional Leydig cells are of higher density, probably related to their extensive endoplasmic reticulum and mitochondria; c) established in vitro cultures of adult and fetal Leydig cell and investigated gonadotropin-dependent regulatory mechanisms; d) demonstrated that a 27,000 protein is induced by estradiol and that similar protein is produced in the Leydig cell during hCG stimulation. This protein could in turn serve to regulate microsomal enzymatic activities.